In the most preferable circumstances the seawater in the lagoon is around 15°-19°C and the hot tubs are around 30°-39°C hot. The lagoon and the hot tubs are heated up with the same kind of water as was in the hot stream, Heiti lækurinn, before. The water comes from the hot water tanks, that are underneath the dome Perlan, and has been used previously to heat up people‘s houses in Reykjavík.